Seat track mechanism for vehicle

ABSTRACT

A seat track mechanism for a vehicle, includes a lower rail mounted to a vehicle floor; an upper rail supported by the lower rail and slidable relative to the lower rail; and spherical rotators held between the lower and upper rails, the spherical rotators rolling via a sliding movement of the upper rail. One of the upper rail and the lower rail includes at least one horizontal flat portion parallel to a widthwise direction of the seat track mechanism and parallel to a direction of the sliding movement of the upper rail, and the other of the upper rail and the lower rail includes at least one rotator supporting recess having a circularly arcuate shape in cross section which is uniform in a lengthwise direction of the seat track mechanism, the spherical rotators being held between the rotator supporting recess and the horizontal flat portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seat track mechanism for a vehiclesuch as an automobile. The seat track mechanism supports a vehicle seatand allows the vehicle seat to be moved forward and rearward foradjustment.

2. Description of the Related Art

A conventional seat track mechanism in which spherical rotators (balls)are installed between a pair of lower rails (lower tracks) and a pair ofupper rails (upper tracks) to smooth the sliding movement of the upperrails relative to the lower rails is known in the art. This type of seattrack mechanism is disclosed in Japanese unexamined patent publicationNo. 2005-47347.

FIG. 16 shows a cross sectional view of a conventional seat trackmechanism by way of example, taken along a vertical plane orthogonal tothe sliding direction of an upper rail (upper track). A lower rail 40that is fixed to a vehicle floor (floor surface) is in the shape of ahollow box, the top of which is open. The lower rail 40 includes abottom portion 40 a, a pair of (left/right) side wall portions 40 b, apair of inward-extending flanges 40 c and a pair of downward-extendingflanges 40 d, wherein the pair of side wall portions 40 b extendupwardly from the lateral edges of the bottom portion 40 a, the pair ofinward-extending flanges 40 c extend inwardly from the top edges of theside wall portions 40 b, and the pair of downward-extending flanges 40 dextend downwardly from the inner edges of the pair of inward-extendingflanges 40 c. The upper rail 41 includes a top portion 41 a, a pair of(left/right) vertical wall portions 41 b, a pair of (left/right) firstinclined portions 41 c and a pair of (left/right) second inclinedportions 41 d, wherein the pair of vertical wall portions 41 b extenddownwardly from the lateral edges of the top portion 41 a, the pair offirst inclined portions 41 c extend obliquely toward the adjacent sidewall portions 40 b from the bottom edges of the pair of vertical wallportions 41 b, the pair of second inclined portions 41 d extendobliquely upwards from the outer edges of the pair of first inclinedportions 41 c. Each of the pair of first inclined portions 41 c isinclined upwardly in a direction from the boundary between the firstinclined portion 41 c and the associated vertical wall portion 41 b(i.e., from the widthwise center of the upper rail 41) toward theadjacent side wall portion 40 b. Each of the pair of second inclinedportions 41 d is inclined upwardly in a direction away from the boundarybetween the second inclined portion 41 d and the associated firstinclined portion 41 c toward the widthwise center of the upper rail 41.Two pairs (left/right pairs) of balls 42 and 43 are installed betweenthe lower rail 40 and the upper rail 41, respectively. Each ball 42 isinscribed in the boundary between the bottom portion 40 a and theadjacent side wall portion 40 b of the lower rail 40 and also in contactwith the adjacent first inclined portion 41 c of the upper rail 41. Eachball 43 is inscribed in the boundary between the adjacent side wallportion 40 b and the adjacent inward-extending flanges 40 c of the lowerrail 40 and also in contact with the adjacent second inclined portion 41d of the upper rail 41. Accordingly, in the seat track mechanism shownin FIG. 16, the four balls 42 and 43 are installed to be inscribed infour corners of the inner surface of the box-shaped lower rail 40 to bepressed against these four corners so that the upper rail 41 isindirectly supported by the lower rail 40 via the four balls 42 and 43at the four corners. If a moving force in the forward/rearward directionis given to the upper rail 41, the upper rail 41 moves in theforward/rearward direction relative to the lower rail 40 while rolling(rotating) the four balls 42 and 43.

In this type of seat track mechanism using balls in the manner as shownin FIG. 16, there is a problem with the working accuracies of the lowerrail 40 and the upper rail 41 being apt to exert an influence on thepositional accuracy and the sliding performance of the upper rail 41.Specifically, the heightwise position of the upper rail 41 with respectto the lower rail 40 is determined by the engagements of the left/rightfirst inclined portions 41 c with the two balls 42; however, if thepoints of contact of the pair of first inclined portions 41 c relativeto the balls 42 in the rail widthwise direction (left/right directionwith respect to FIG. 16) vary, the heightwise position of the upper rail41 varies because the left/right first inclined portions 41 c areinclined to both the horizontal and vertical directions. In addition,since a force urging each ball 42 to be held at a balancing positionrelative to the associated first inclined portion 41 c is produced, theupper rail 41 easily tilts when the bilaterally symmetrical shapes ofthe left/right first inclined portions 41 c relative to the railwidthwise direction are not properly maintained or when a slanting(rotational) force along the first inclined portions 41 c acts on theupper rail 41. Additionally, the downward load acting on the upper rail41 is received by the pair of first inclined portions 41 c and the balls42; however, a component force urging the pair of vertical wall portions41 b to approach each other along the inclinations of the left/rightfirst inclined portions 41 c is produced if a downward load is imposedon the upper rail 41 from the top portion 41 a when, e.g., an occupantsits in the seat on the upper rail 41. If the upper rail 41 is deformedby this component force, there is a possibility that the sliding loadbecomes too light or play occurs between the upper rail 41 and the lowerrail 40 and between the upper rail 41 and the balls 42 and 43.

Additionally, not only a downward load but also an upward load acts onthe seat track mechanism via a seatbelt anchor and the like. In the seattrack mechanism shown in FIG. 16, a load in a direction to pull up theupper rail 41 is received by the balls 43 via the left/right secondinclined portions 41 d. Since the second inclined portions 41 d areinclined to both the horizontal and vertical directions, a componentforce in a horizontal direction is produced due to the inclination ofthe left/right second inclined portions 41 d if a load in the upwarddirection with respect to FIG. 16 acts on the upper rail 41. Thiscomponent force acts on the upper rail 41 to urge the pair of verticalwall portions 41 b to approach each other and also acts on the lowerrail 40 to urge the pair of side wall portions 40 b to move away fromeach other. If the positions of the upper rail 41 and the lower rail 40change according to this component force, the force to hold the balls 42and 43 becomes weak, so that the upper rail 41 becomes unsteady.

In a seat track mechanism for an automobile which supports a vehicleseat and allows the vehicle seat to be moved forward and rearward foradjustment, a pair of upper rails fixed to the bottom of the vehicleseat are supported by a pair of lower rails fixed to a vehicle floor tobe slidable relative to the pair of lower rails, respectively. Althoughmainly a downward load due to the weight of the seated occupant and theweight of the vehicle seat itself acts on the pair of upper rails undernormal usage conditions, an upward tensile load (pulling load) acts on aseatbelt anchor fixed to one of the pair of upper rails if the seatbeltis pulled strongly at a time of, e.g., collision of the vehicle. Toprevent the upper rail, having the seatbelt anchor, from being detachedfrom the associated lower rail to protect the seated occupant upon suchan upward tensile load acting on the seatbelt anchor, the seat trackmechanism is designed to have an anti-detaching structure preventing theupper rail from moving upward relative to the lower rail. A seat trackmechanism with such an anti-detaching structure is known in the art inwhich a pair of anti-detaching flanges, such as the inward-extendingflanges 40 c of FIG. 16, are formed on the top side of a lower rail thathas a box-shaped cross section and in which a corresponding pair ofanti-detaching portions which come in contact with the pair ofanti-detaching flanges of the lower rail from below are formed on theassociated upper rail in a manner such as disclosed in Japaneseunexamined patent publication NO. 2003-72432.

Due to the structure of a seatbelt, the pulling load that is imposed onthe seatbelt anchor-bearing upper rail via the seatbelt and the seatbeltanchor acts on the seatbelt anchor-bearing upper rail in an upwarddirection slightly inclined to the vertical direction. In an upper railprovided in the widthwise center thereof with a portion having aninverted U-shaped cross section and further provided at the oppositeends of this central portion in the widthwise direction of the upperrail with two anti-detaching portions, respectively, i.e., in a type ofupper rail having a hat-shaped (Ω-shaped) cross section such asdisclosed in Japanese unexamined patent publication No. 2003-72432,there is a possibility of the upper rail being deformed in a manner tomake a central portion of the upper rail become narrower (to narrow thewidth of the central portion of the upper rail) when the upper rail isacted upon by a pulling load in a direction obliquely upward via theanti-detaching portions. If this sort of deformation appears, thestrength of the upper rail decreases or the upper rail becomes unsteadywhen the upper rail slides on the lower rail, and accordingly, it isnecessary to take such measures as a measure to provide theaforementioned seatbelt anchor-bearing upper rail therein with areinforcing member or the like which prevents this upper rail from beingdeformed.

SUMMARY OF THE INVENTION

The present invention provides a seat track mechanism in which an upperrail is supported by a lower rail to be slidable on the lower rail viaspherical rotators, wherein the seat track mechanism is simple instructure, the positional deviation of the upper rail relative to thelower rail does not easily occur, and the upper rail does not easilybecome unsteady when the upper rail slides on the lower rail.

In addition, the present invention provides a seat track mechanism whichis designed so that the strength of the upper rail and the slidingperformance thereof are not easily impaired upon a pulling load (upwardtensile load) in an upward direction slightly inclined to the verticaldirection being imposed on the upper rail.

According to an aspect of the present invention, a seat track mechanismfor a vehicle is provided, including a lower rail mounted to a vehiclefloor; an upper rail supported by the lower rail to be slidable relativeto the lower rail; and spherical rotators held between the lower railand the upper rail, wherein the spherical rotators roll according to asliding movement of the upper rail. One of the upper rail and the lowerrail includes at least one horizontal flat portion substantiallyparallel to a widthwise direction of the seat track mechanism andsubstantially parallel to a direction of the sliding movement of theupper rail. The other of the upper rail and the lower rail includes atleast one rotator supporting recess having a circularly arcuate shape incross section which is uniform in a lengthwise direction of the seattrack mechanism, the spherical rotators being held between the rotatorsupporting recess and the horizontal flat portion.

It is desirable for a radius of curvature of a circularly-arcuate innerperipheral surface of the rotator supporting recess to be greater than aradius of curvature of the spherical rotators.

It is desirable for the rotator supporting recess to be formed at a baseof the lower rail, and for the horizontal flat portion to be formed onthe upper rail.

It is desirable for a pair of the horizontal flat portions to beprovided at different positions in a widthwise direction of the upperrail, and for a pair of the rotator supporting recesses to be providedat corresponding different positions in a widthwise direction of thelower rail.

It is desirable for each of the spherical rotators to be a metal ball.

It is desirable for the rotator supporting recess to be recessed in adirection away from the horizontal flat portion.

It is desirable for the rotator supporting recess and the horizontalflat portion to face each other in a vertical direction of the seattrack mechanism.

It is desirable for the seat track mechanism to include at least oneguide rod for supporting the spherical rotators which is installedbetween the rotator supporting recess and the horizontal flat portion,the guide rod extending parallel to both the upper rail and the lowerrail, wherein the guide rod includes through holes in which thespherical rotators are engaged, respectively, so that relative positionsbetween the spherical rotators in the direction of the sliding movementof the upper rail are maintained constant.

According to another aspect of the present invention, the upper railincludes a central portion having an inverted U-shaped cross section,and two anti-detaching portions which are formed on opposite sides ofthe central portion in a widthwise direction thereof to prevent theupper rail from being detached from the lower rail. The twoanti-detaching portions apply a component force on the central portionso as to urge the central portion to increase a width thereof byabutting against two flanges formed on the lower rail, respectively,when a pulling load in a direction obliquely upward and lateral isimposed on the upper rail.

It is desirable for each the two anti-detaching portions to produce acomponent force urging a free end thereof that abuts against associatedone of the two flanges to tilt toward a widthwise center of the upperrail about an axis substantially parallel to a lengthwise direction ofthe upper rail when the pulling load is imposed on the upper rail.

It is desirable for the free end of each anti-detaching portion of theupper rail to be positioned closer to the central portion of the upperrail than the axis, and for an angle of a line connecting the free endof each anti-detaching portion with the axis relative to a verticaldirection to be greater than an angle of the direction of the pullingload.

It is desirable for the lower rail to include two deformation preventiveportions which are positioned adjacent to the opposite sides of thecentral portion of the upper rail to prevent the width of the centralportion of the upper rail from increasing.

It is desirable for the two anti-detaching portions of the upper rail tobe provided as a pair which are respectively positioned on oppositesides of the central portion of the upper rail in the widthwisedirection thereof to be substantially bisymmetrical to each other.

It is desirable for the central portion and the two anti-detachingportions of the upper rail to be formed to have an Ω-shaped crosssection taken along a plane orthogonal to a direction of slidingmovement of the upper rail relative to the lower rail.

According to an aspect of the present invention, a seat track mechanismcan be achieved in which a simple structure improves the accuracy andthe strength of a rotator supporting structure of the seat trackmechanism, effectively prevents the positional deviation of the upperrail relative to the lower rail from occurring, and effectively preventsthe upper rail from becoming unsteady when the upper rail slides on thelower rail.

According to an aspect of the present invention, a seat track mechanismcan be achieved in which the strength of the upper rail and the slidingperformance thereof are not easily impaired upon a pulling load (upwardtensile load) in an upward direction slightly inclined to the verticaldirection being imposed on the upper rail.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is a side elevational view of a vehicle seat assembly including afirst embodiment of a seat track mechanism according to the presentinvention;

FIG. 2 is an exploded perspective view of the seat track mechanism shownin FIG. 1;

FIG. 3 is a cross sectional view of the first embodiment of the seattrack mechanism, taken along a vertical plane substantially orthogonalto the sliding direction of an upper rail;

FIG. 4 is an enlarged cross sectional view of a portion of the seattrack mechanism shown in FIG. 3, showing a left side of the seat trackmechanism;

FIG. 5 is an enlarged cross sectional view of a portion of the seattrack mechanism shown in FIG. 3, showing a ball holding structure forholding a ball between a first ball contacting portion of the upper railand a ball-supporting recessed portion of the associated lower rail;

FIG. 6 is a perspective view of a portion of a type of ball guide whichincludes a resistance protrusion;

FIG. 7 is a side view, partly omitted, of the ball guide;

FIG. 8 is a plan view, partly omitted, of the ball guide;

FIG. 9 is a cross sectional view taken along the IX-IX line shown inFIG. 8, viewed in the direction of the appended arrows;

FIG. 10 is a cross sectional view of the first embodiment of the seattrack mechanism, taken at the position of a ball-guide movement limitportion formed between the upper rail and the lower rail;

FIG. 11 is a side elevational view of a vehicle seat assembly includinga second embodiment of the seat track mechanism according to the presentinvention;

FIG. 12 is an exploded perspective view of a combination of an upperrail and a lower rail of the seat track mechanism shown in FIG. 11;

FIG. 13 is a perspective view of the upper rail and the lower rail shownin FIG. 12 in a combined state;

FIG. 14 is a cross sectional view of the combination of the upper railand the lower rail shown in FIG. 13, taken along a vertical planeorthogonal to the sliding direction of the upper rail;

FIG. 15 is a cross sectional view of a comparative example of acombination of an upper rail and a lower rail which is to be comparedwith the second embodiment of the seat track mechanism; and

FIG. 16 is a cross sectional view of a conventional seat trackmechanism, taken along a vertical plane substantially orthogonal to thesliding direction of the upper rail.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a vehicle seat assembly 10 including a first embodiment ofa seat track mechanism according to the present invention. The firstembodiment of the seat track mechanism will be hereinafter discussedwith reference to FIGS. 1 through 10. The vehicle seat assembly 10 isprovided with a seat cushion 11 that supports buttocks of the occupantwho is seated in the vehicle seat, and a seatback 12 that supports theback of the seated occupant. The vehicle seat assembly 10 is supportedby a seat track mechanism 13 to be movable in the forward/rearwarddirection relative to a vehicle floor (floor surface) 14. The seat trackmechanism 13 is provided with an upper rail 15 and a lower rail 16, soas to constitute a pair of rails which are secured to the bottom of theseat cushion 11 and the vehicle floor 14, respectively. As shown in FIG.2, the seat track mechanism 13 is provided between the upper rail 15 andthe lower rail 16 with metal balls (spherical rotators) 17 and 18. Theupper rail 15 and the lower rail 16 are elongated in theforward/rearward direction of the vehicle, and the position of the seatcushion 11 in the forward/rearward direction can be adjusted by slidingthe upper rail 15 relative to the lower rail 16. The upper rail 15 isprovided thereon with a seatbelt anchor (L-shaped anchor plate) 31 (seeFIG. 1) to which a seatbelt 30 is connected. Although only a pair ofrails (the upper rail 15 and the lower rail 16) is shown in FIG. 2, theseat track mechanism 13 is provided with two pairs of rails (each ofwhich includes the upper rail 15 and the lower rail 16) installed atdifferent positions in the left/right direction (lateral direction) ofthe vehicle seat assembly 10 to extend parallel to each other.

As shown in FIGS. 3 and 4, the lower rail 16 is provided with a bottomportion 16 a, a pair of (left/right) side wall portions 16 b, a pair ofinward-extending flanges 16 c and a pair of downward-extending flanges16 d. The bottom portion 16 a faces the vehicle floor 14, the pair ofside wall portions 16 b extend upwardly from the lateral edges of thebottom portion 16 a, the pair of inward-extending flanges 16 c extendinwardly, toward a center of the upper rail 15 and the lower rail 16 inthe left/right direction with respect to FIG. 3 (hereinafter referred toas a rail center), from the top edges of the side wall portions 16 b,and the pair of downward-extending flanges 16 d extend downwardly fromthe inner edges (edges closer to the rail center) of the pair ofinward-extending flanges 16 c.

A central portion of the bottom portion 16 a is formed as a horizontalflat bottom portion 16 a-1. The bottom portion 16 a is provided, on bothsides of this central portion of the bottom portion 16 a, with a pair ofball-supporting recessed portions (rotator supporting recesses) 16 a-2,respectively. Each ball-supporting recessed portion 16 a-2 has acircularly arcuate shape in cross section which is uniform in thelengthwise direction of the lower rail 16, and a total of four balls 17are positioned on the arc-shaped inner peripheral surface of eachball-supporting recessed portion 16 a-2 to be supported thereby. Asshown in FIG. 5, a radius of curvature CR1 of the inner peripheralsurface of each ball-supporting recessed portion 16 a-2 is greater thana radius of curvature CR2 of the spherical surface of each ball 17, andaccordingly, each ball 17 is in point contact with the inner peripheralsurface of the associated ball-supporting recessed portion 16 a-2 to besupported thereby at a single point thereon. In addition, the innersurface of the boundary between each side wall portion 16 b and theassociated inward-extending flange 16 c is formed as a ball inscribingsurface 16 e having an arc-shaped cross section.

The upper rail 15 is provided with a top portion 15 a, a pair of(left/right) vertical wall portions 15 b, a pair of (left/right) firstball contacting portions (horizontal flat portions) 15 c, a pair of(left/right) connecting portions 15 d and a pair of (left/right) secondball contacting portions 15 e. The pair of vertical wall portions 15 bextend downwardly from the lateral edges of the top portion 15 a, thepair of first ball contacting portions 15 c extend sideways, toward theadjacent side wall portions 16 b, from the bottom edges of the pair ofvertical wall portions 15 b, the pair of connecting portions 15 d extendupwardly from the outer edges of the pair of first ball contactingportions 15 c, and the pair of second ball contacting portions 15 eextend obliquely upwards, toward the pair of downward-extending flanges16 d, from the top edges of the pair of connecting portions 15 d. In theupper rail 15, the top portion 15 a and the first ball contactingportions 15 c are formed as horizontal flat portions substantiallyorthogonal to a load in a vertical direction (i.e., substantiallyparallel to the widthwise direction of the upper rail 15), and thevertical wall portions 15 b and the connecting portions 15 d are formedas vertical flat portions substantially orthogonal to the horizontalflat portions. Each second ball contacting portion 15 e is formed as aninclined flat portion which approaches the associated vertical wallportion 15 b (i.e., toward the rail center) in the upward direction fromthe boundary between the second ball contacting portion 15 e and theassociated connecting portion 15 d.

As shown in FIG. 3, the upper rail 15 is installed in the lower rail 16so that the pair of vertical wall portions 15 b are positioned betweenthe pair of downward-extending flanges 16 d with the top portion 15 abeing orientated upwardly and so that the pair of connecting portions 15d are positioned between the pair of side wall portions 16 b. In a statewhere the upper rail 15 and the lower rail 16 are combined, each firstball contacting portion 15 c and the associated ball-supporting recessedportion 16 a-2 face each other and are spaced from each other in thevertical direction, while each second ball contacting portion 15 e andthe associated ball inscribing surface 16 e face each other and arespaced from each other in a direction substantially orthogonal to thedirection of inclination of the second ball contacting portion 15 e.Four balls 17 are held between each first ball contacting portion 15 cand the associated ball-supporting recessed portion 16 a-2 to be allowedto roll in the space therebetween, while four ball 18 are held betweeneach second ball contacting portion 15 e and the associated ballinscribing surface 16 e to be allowed to roll in the space therebetween.

The balls 17 are installed in between the upper rail 15 and the lowerrail 16 while being supported by resin-molded ball guides 20, and alsothe balls 18 are installed in between the upper rail 15 and the lowerrail 16 while being supported by resin-molded ball guides 21 (21P or21M).

As shown in FIG. 2, the ball guides 20 are provided as a pair (left andright ball guides) for each combination of the upper rail 15 and thelower rail 16, and the ball guides 20 are shaped into rods extending inthe lengthwise direction of the seat track mechanism 13. Each ball guide20 is provided at four different positions thereon in the lengthwisedirection of the ball guide 20 with four ball supporting holes 20 a forsupporting four balls 17, respectively. Two of the four ball supportingholes 20 a and the remaining two ball supporting holes 20 a are formedat the opposite ends of each ball guide 20, respectively. In FIG. 2,regarding one of the two ball guides 20, only a portion of the ballguide 20 in the vicinity of one of the opposite ends thereof whichincludes two ball supporting holes 20 a is shown.

Similar to the ball guides 20, the seat track mechanism 13 is providedwith the aforementioned ball guides 21 (21P or 21M) as a pair (left andright ball guides) for each combination of the upper rail 15 and thelower rail 16, and the ball guides 21 are shaped into rods extending inthe lengthwise direction of the seat track mechanism 13. Each ball guide21 is provided at four different positions thereon in the lengthwisedirection of the ball guide 21 with four ball supporting holes 21 a forsupporting four balls 18, respectively. Two of the four ball supportingholes 21 a and the remaining two ball supporting holes 21 a are formedat the opposite ends of each ball guide 21, respectively.

Each ball guide 20 is inserted into the space between one of the pair offirst ball contacting portions 15 c and the associated ball-supportingrecessed portion 16 a-2 with four balls 17 being respectively engaged inthe four ball supporting holes 20 a of the ball guide 20 to be supportedthereby, and each ball guide 21 is inserted into the space between oneof the pair of second ball contacting portions 15 e and the associatedball inscribing surface 16 e with four balls 18 being respectivelyengaged in the four ball supporting holes 21 a of the ball guide 21 tobe supported thereby. Each of the ball supporting holes 20 a and 21 a isa through hole. In a state where the ball guides 20 and 21 are insertedin the aforementioned associated spaces between the upper rail 15 andthe lower rail 16, each ball 17 projects upward and downward from theassociated ball supporting hole 20 a of the ball guide 20 to be incontact with the associated first ball contacting portion 15 c and theassociated ball-supporting recessed portion 16 a-2, respectively, whileeach ball 18 projects upward and downward from the associated ballsupporting hole 21 a of the ball guide 21 to be in contact with theassociated second ball contacting portion 15 e and the associated ballinscribing surface 16 e, respectively.

The seat track mechanism 13 is provided with movement limit portions forlimiting the maximum amount of movement of the ball guides 20 and 21 inthe sliding direction thereof. As shown in FIGS. 2 and 10, the upperrail 15 is provided, on the pair of second ball contacting portions 15 eat different positions in the forward/rearward direction, with a pair offront movement limit lugs 15 f-F (as forward movement limit portions forthe ball guides 21) and a pair of rear movement limit lugs 15 f-R (asrearward movement limit portions for the ball guides 21) in the vicinityof the front end and the rear end of the upper rail 15, respectively,and the lower rail 16 is provided on the pair of side wall portions 16 bat different positions in the forward/rearward direction, with a pair offront bent lugs 16 f-F (as forward movement limit portions for the ballguides 21) and a pair of rear bent lugs 16 f-R (as rearward movementlimit portions for the ball guides 21) in the vicinity of the front endand the rear end of the lower rail 16, respectively. As shown in FIG.10, each movement limit lug of the front movement limit lugs 15 f-F andthe rear movement limit lugs 15 f-R is provided in the vicinity of theupper end thereof with a protruding portion which protrudes obliquelyupwards and inwards. This protruding portion of each movement limit lug15 f-F and 15 f-R lies on the moving path of the associated ball guide21. The relative positions between the movement limit lugs 15 f-F and 15f-R of the upper rail 15 and the bent lugs 16 f-F and 16 f-R of thelower rail 16 are determined so that the movement limit lugs 15 f-F and15 f-R and the bent lugs 16 f-F and 16 f-R do not interfere with eachother when the upper rail 15 slides on the lower rail 16 via the balls17 under normal conditions (see FIG. 10).

When the upper rail 15 is in the central position (neutral position)between the front and rear ends (opposite ends) of the moving range ofthe upper rail 15 with respect to the lower rail 16, the front movementlimit lugs 15 f-F are positioned behind the front bent lugs 16 f-F to beadjacent thereto while the rear movement limit lugs 15 f-R arepositioned in front of the rear bent lugs 16 f-R to be adjacent thereto.From this position, moving the upper rail 15 forward relative to thelower rail 16 causes the rear movement limit lugs 15 f-R of the upperrail 15 to approach the front bent lugs 16 f-F of the lower rail 16. Thedistance between the front bent lugs 16 f-F and the rear movement limitlugs 15 f-R in the forward/rearward direction is determined so that theball guides 21 having moved forward with the upper rail 15 are heldbetween the front bent lugs 16 f-F and the rear movement limit lugs 15f-R with the front and rear ends of the ball guides 21 being in contactwith the front bent lugs 16 f-F and the rear movement limit lugs 15 f-R,respectively, when the upper rail 15 moves to the front limit ofmovement thereof. At this time, the forward sliding movement of the ballguides 21 relative to the lower rail 16 is limited by the front bentlugs 16 f-F and the rearward sliding movement of the ball guides 21relative to the lower rail 16 is limited by the rear movement limit lugs15 f-R. Additionally, moving the upper rail 15 rearward relative to thelower rail 16 causes the front movement limit lugs 15 f-F of the upperrail 15 to approach the rear bent lugs 16 f-R of the lower rail 16. Thedistance between the front movement limit lugs 15 f-f and the rear bentlugs 16 f-R in the forward/rearward direction is determined so that theball guides 21 having moved rearward with the upper rail 15 are heldbetween the front movement limit lugs 15 f-F and the rear bent lugs 16f-R with the front and rear ends of the ball guides 21 being in contactwith the front movement limit lugs 15 f-F and the rear bent lugs 16 f-R,respectively, when the upper rail 15 moves to the rear limit of movementthereof. At this time, the forward sliding movement of the ball guides21 relative to the lower rail 16 is limited by the front movement limitlugs 15 f-F and the rearward sliding movement of the ball guides 21relative to the lower rail 16 is limited by the rear bent lugs 16 f-R.

As shown in FIG. 10, the upper rail 15 is provided, on the pair of firstball contacting portions 15 c at different positions in theforward/rearward direction, with a pair of front movement limitprojections 15 g-F (as forward movement limit portions for the ballguides 20) and a pair of rear movement limit projections 15 g-R (asrearward movement limit portions for the ball guides 20) in the vicinityof the front end and the rear end of the upper rail 15, respectively,and the lower rail 16 is provided at different positions in theforward/rearward direction with a pair of front inwardly bent portions16 g-F (as forward movement limit portions for the ball guides 20) and apair of rear inwardly bent portions 16 g-R (as rearward movement limitportions for the ball guides 20) in the vicinity of the front end andthe rear end of the lower rail 16, respectively (see FIGS. 2 and 10).Note that the front movement limit projections 15 g-F and the rearmovement limit projections 15 g-R do not appear in FIG. 2 and are shownonly in the cross sectional view in FIG. 10. The front movement limitprojections 15 g-F and the rear movement limit projections 15 g-R areprovided separately from each other in the forward/rearward direction,just as with the front movement limit lugs 15 f-F and the rear movementlimit lugs 15 f-R. Specifically, the front movement limit projections 15g-F are formed at substantially the same front positions as the frontmovement limit lugs 15 f-F in the lengthwise direction of the upper rail15, and the rear movement limit projections 15 g-R are formed atsubstantially the same rear positions as the rear movement limit lugs 15f-R in the lengthwise direction of the upper rail 15. The front movementlimit projections 15 g-F and the rear movement limit projections 15 g-Rare formed to project downward from the first ball contacting portions15 c to lie on the moving paths of the ball guides 20. Additionally, asshown in FIG. 10, the front inwardly bent portions 16 g-F and the rearinwardly bent portions 16 g-R are formed by inwardly bending portions ofthe lower rail 16 at the boundaries between the side wall portions 16 band the bottom portion 16 a to lie on the moving paths of the ballguides 20. The distance between the front inwardly bent portions 16 g-Fand the rear inwardly bent portions 16 g-R in the forward/rearwarddirection is substantially identical to the distance between the frontbent lugs 16 f-F and the rear bent lugs 16 f-R. The relative positionsbetween the movement limit projections 15 g-F and 15 g-R of the upperrail 15 and the inwardly bent portions 16 g-F and 16 g-R of the lowerrail 16 are determined so that the movement limit projections 15 g-F and15 g-R and the inwardly bent portions 16 g-F and 16 g-R do not interferewith each other when the upper rail 15 slides on the lower rail 16 viathe balls 17 under normal conditions (see FIG. 10).

When the upper rail 15 is in the central position (neutral position)between the front and rear ends (opposite ends) of the moving range ofthe upper rail 15 with respect to the lower rail 16, the front movementlimit projections 15 g-F are positioned behind the front inwardly bentportions 16 g-F to be adjacent thereto while the rear movement limitprojections 15 g-R are positioned in front of the rear inwardly bentportions 16 g-R to be adjacent thereto. From this state, moving theupper rail 15 forward relative to the lower rail 16 causes the rearmovement limit projections 15 g-R of the upper rail 15 to approach thefront inwardly bent portions 16 g-F of the lower rail 16. The distancebetween the front inwardly bent portions 16 g-F and the rear movementlimit projections 15 g-R in the forward/rearward direction is determinedso that the ball guides 20 having moved forward with the upper rail 15are held between the front inwardly bent portions 16 g-F and the rearmovement limit projections 15 g-R with the front and rear ends of theball guides 20 being in contact with the front inwardly bent portions 16g-F and the rear movement limit projections 15 g-R, respectively, whenthe upper rail 15 moves to the front limit of movement thereof. At thistime, the forward sliding movement of the ball guides 20 relative to thelower rail 16 is limited by the front inwardly bent portions 16 g-F, andthe rearward sliding movement of the ball guides 20 relative to thelower rail 16 is limited by the rear movement limit projections 15 g-R.Additionally, moving the upper rail 15 rearward relative to the lowerrail 16 causes the front movement limit projections 15 g-F of the upperrail 15 to approach the rear inwardly bent portions 16 g-R of the lowerrail 16. The distance between the front movement limit projections 15g-F and the rear inwardly bent portions 16 g-R in the forward/rearwarddirection is determined so that the ball guides 20 having moved rearwardwith the upper rail 15 are held between the front movement limitprojections 15 g-F and the rear inwardly bent portions 16 g-R with thefront and rear ends of the ball guides 20 being in contact with thefront movement limit projections 15 g-F and the rear inwardly bentportions 16 g-R, when the upper rail 15 moves to the rear limit ofmovement thereof. At this time, the forward sliding movement of the ballguides 20 relative to the lower rail 16 is limited by the front movementlimit projections 15 g-F, and the rearward sliding movement of the ballguides 21 relative to the lower rail 16 is limited by the rear inwardlybent portions 16 g-R.

As shown in FIG. 2, there are previously prepared two types of ballguides: a pair of ball guides 21P each of which includes a resistanceprotrusion 21 c, and a pair of ball guides 21M neither of which includesthe resistance protrusion 21 c. The pair of ball guides 21P and the pairof ball guides 21M are selectively installed as required.

As shown in FIGS. 6 through 8, each ball guide 21P is provided, on thetop surface thereof that faces the associated ball inscribing surface 16e, with a rib-shaped projection 21 b which projects in a direction awayfrom the associated second ball contacting portion 15 e and which iselongated along the lengthwise direction of the ball guide 21P, and eachball guide 21P is further provided, on a central portion of the topsurface of the ball guide 21P in the lengthwise direction thereof, withthe aforementioned resistance protrusion 21 c which projects in the samedirection as the associated rib-shaped projection 21 b by a greateramount than the associated rib-shaped projection 21 b (to be closer tothe associated ball inscribing surface 16 e than the associatedrib-shaped projection 21 b). As shown in FIGS. 4 and 9, the amount ofprojection of the resistance protrusion 21 c is predetermined so thatthe top end of the resistance protrusion 21 c projects slightly from theouter spherical surfaces of the associated balls 18 as viewed from thefront of the associated ball guide 21 in a free state before theresistance protrusion 21 c is deformed. Upon the pair of ball guides 21Pbeing respectively inserted into the two spaces between the pair ofsecond ball contacting portions 15 e and the pair of ball inscribingsurfaces 16 e with four balls 18 being engaged in the four ballsupporting holes 21 a of each ball guide 21, the resistance protrusion21 c of each ball guide 21 is compressed and deformed between theassociated contacting surface 16 e and the associated second ballcontacting portion 15 e so that both the resistance protrusion 21 c andthe associated balls 18 come in contact with the associated ballinscribing surface 16 e. Due to the sliding friction given by theresistance protrusion 21 c thus deformed, the sliding load (resistance)increases when the upper rail 15 slides. Although only the resistanceprotrusion 21 c appears to be in contact with the associated ballinscribing surface 16 e in FIG. 4 since the resistance protrusion 21 cin a free state before being compressed and deformed is shown in FIG. 4,not only the resistance protrusion 21 c but also the balls 18 come incontact with the associated ball inscribing surface 16 e with theresistance protrusion 21 c being compressed and deformed in reality whenthe ball guides 21P are installed in place.

On the other hand, each ball guide 21M is provided with a rib-shapedprojection 21 b just as with each ball guide 21P, but is not providedwith the resistance protrusion 21 c that each ball guide 21P has. Whenthe pair of ball guides 21M are respectively installed in between thepair of second ball contacting portions 15 e and the pair of ballinscribing surfaces 16 e with four balls 18 being engaged in the fourball supporting holes 21 a of each ball guide 21, the rib-shapedprojection 21 b of each ball guide 21M does not come in contact with theassociated ball inscribing surface 16 e, so that the sliding resistancebecomes smaller than that in the case of using the ball guides 21P.

It is desirable to use the pair of ball guides 21P and the pair of ballguides 21M appropriately according to the seat slide mechanism (notshown) used for sliding the upper rail 15.

Two types of seat slide mechanisms are known in the art, i.e., a powerslide mechanism (motor-driven slide mechanism) and a manual slidemechanism. However, in conventional seat track mechanisms, a constantsliding resistance is not always applied to forward/rearward movementsof the seat; the load on forward/rearward movements of the seat differsaccording to whether the seat moves forward or rearward in the casewhere each seat rail is inclined so that the levels of the front andrear ends of each seat rail are mutually different. In such a case, ifthe seat slide mechanism is a power slide type of seat slide mechanism,the motor driving sound varies by variations in load on a motor causedaccording to whether the seat is driven forward or rearward. To reducevariations of the motor driving sound, it is desirable that the slidingresistance of the upper rail 15 with respect to the lower rail 16 be setat a high resistance in advance so that the difference between thesliding resistance at the time the seat moves forward and the slidingresistance at the time seat moves rearward becomes small. Increasing theball diameter and also tuning the seat rail shape itself by adjustingthe amount of warping of the upper rail are known methods for increasingthe sliding resistance. However, a resistance to the balls is a rollingfriction, so that the friction coefficient is small, and accordingly, itis difficult to increase the sliding resistance in an effective mannersimply by increasing the ball diameter. In addition, if the diameters ofthe balls 17 and 18 are increased excessively, there is a possibility ofthe heightwise position of the upper rail 50 with respect to the lowerrail 60 changing. Additionally, it is time-consuming to tune the amountof warping of the upper rail (i.e., to adjust the amount of warping ofthe upper rail for precise functioning) that is made of metal as arelatively large member; moreover, there is a possibility of the upperrail interfering with the lower rail if the degree of tuning isinappropriate. In contrast, since the resistance protrusions 21 c ofeach ball guide 21 that is in line (or surface) contact with the ballinscribing surface 16 e of the associated lower rail 16 in an areathereon extending in the lengthwise direction of the seat trackmechanism 13 exerts a sliding resistance on the ball inscribing surface16 e of the associated lower rail 16, so that the friction coefficientis large, and accordingly, the sliding resistance can be easilyincreased in an effective manner at little expense in time and effort.

In the case where the seat slide mechanism is a manual slide type ofseat slide mechanism, variations of such a sound as the motor drivingsound produced by the power slide type of seat slide mechanism do nothave to be taken into account and it is undesirable for the slidingresistance to be high when the seat is manually moved, and accordingly,it is desirable for the ball guides 21M, each of which does not includethe resistance protrusion 21 c, to be used in the slide track mechanism13.

Namely, an appropriate sliding resistance can be easily set simply byselecting either the two ball guides 21P or the two ball guides 21M withno need to adjust the amount of warping of the upper rails 15 or preparevarious types of balls 18 having different diameters beforehand. Theball guides 21P and 21M are molded of resin, thus being easy to produceand causing less noise when in use.

Since each of all the four ball guides 20 and 21 (21P or 21M) holds fourballs 17 and 18, respectively, that are aligned in the lengthwisedirection of the seat track mechanism 13, the intervals between theballs in the lengthwise direction of the seat track mechanism 13 can bedetermined with a high degree of precision. Additionally, the pair ofball guides (left and right ball guides) 20 and the pair of ball guides(left and right ball guides) 21 (21P and 21M) are separated from eachother in the widthwise direction of the seat track mechanism 13, i.e.,not connected to each other in the widthwise direction of the seat trackmechanism 13, and therefore do not interfere with other elements of theseat track mechanism 13 which are positioned in a central part of theseat track mechanism 13. For instance, unlike the pair of ball guides 20in the present embodiment of the seat track mechanism 13, a ball guidewhich is shaped to be spread over left and right balls (which correspondto the left and right balls 17) to support these balls is known in theart. However, since this conventional type of ball guide is positionedto overlap protrusions (e.g., stop pins for limiting the amount of railsliding amount) formed at the bottoms of the lower rails in thewidthwise direction of the seat track mechanism, each seat rail (upperand lower rails) is required to secure a long length to be preventedfrom interfering with such protrusions. Accordingly, miniaturization ofthe seat track mechanism is limited by the installation of such aconventional ball guide. In contrast, this sort of interference problemdoes not have to be taken into account and the lengths of the upper andlower rails 15 and 16 can be cut down since the ball guides 20 and theball guides 21 of the present embodiment of the seat track mechanism 13are small in a frontal projected area and do not extend to a centralportion between the upper rails 15 or the lower rails 16 in thewidthwise direction of the seat track mechanism 13.

As described above, in the seat track mechanism 13, the upper rail 15 issupported by the lower rail 16 via the plurality of balls 17 and 18, andmoving the upper rail 15 in the forward/rearward direction causes theballs 17, which are installed between the pair of first ball contactingportions 15 c and the pair of ball-supporting recessed portions 16 a-2,to roll therebetween and simultaneously causes the balls 18, which areinstalled between the pair of (left/right) second ball contactingportions 15 e and the ball inscribing surfaces 16 e of the lower rail16, to roll therebetween, which makes smooth sliding movements of theupper rail 15 relative to the lower rail 16 possible.

As described above, in the present embodiment of the seat trackmechanism 13, the balls 17 are supported by the arc-shaped innerperipheral surfaces of the ball-supporting recessed portions 16 a-2 ofthe lower rail 16, and the contacting portions of the upper rail 15which are in contact with the balls 17 are formed as the pair of firstball contacting portions 15 c that serve as horizontal flat portions.This structure is superior in variation inhibitive control (stability)on the height position of the upper rail 15 with respect to the lowerrail 16 (the distance from the bottom portion 16 a of the lower rail 16to the top portion 15 a) and is also effective in preventing the upperrail 15 from tilting relative to the lower rail 16.

The height position of the upper rail 15 itself does not change even ifthe contact points between the pair of first ball contacting portions 15c and the balls 17 in the widthwise direction of the seat trackmechanism 13 (the left/right direction with respect to FIG. 3) changedue to variations in dimensional accuracies of components of the seattrack mechanism 13, loads in the lateral direction of the seat trackmechanism 13 since the contacting portions of the upper rail 15 whichcome in contact with the balls 17 are formed as the pair of first ballcontacting portions 15 c that serve as horizontal flat portions. Inaddition, on the lower rail 16 side, the pair of ball-supportingrecessed portions 16 a-2, which are positioned below the pair of firstball contacting portions 15 c to face the pair of first ball contactingportions 15 c, constitute support portions for supporting the balls 17.The balls 17, which receive loads from above via the pair of first ballcontacting portions 15 c, try to stay at specific positions on thearc-shaped inner peripheral surfaces of the pair of ball-supportingrecessed portions 16 a-2 in the widthwise direction of the seat trackmechanism 13 (specifically, at the deepest positions in the pair ofball-supporting recessed portions 16 a-2 in the widthwise direction ofthe seat track mechanism 13). Therefore, the positions of the balls 17with respect to the lower rail 16 also become stable. Accordingly,neither of the positions of the balls 17 with respect to the lower rail16 in the vertical direction nor the positions of the pair of first ballcontacting portions 15 c with respect to the balls 17 in the verticaldirection vary easily. In other words, elements which determine theheight position of the upper rail 15 with respect to the lower rail 16are composed of the pair of first ball contacting portions 15 c, whichare horizontal flat portions causing no variations in the heightposition between the pair of first ball contacting portions 15 c and theballs 17, and the pair of ball-supporting recessed portions 16 a-2,which are formed to have concave inner surfaces that make the positionsof the balls 17 easy to settle in position, and accordingly, the heightposition of the upper rail 15 with respect to the lower rail 16 can bestabilized.

In addition, the pair of first ball contacting portions 15 c have thecapability of preventing the upper rail 15 from tilting relative to thelower rail 16 when a tilting load which may rotate the upper rail 15about an axis parallel to the lengthwise direction of the upper rail 15acts on the upper rail 15. In other words, since the pair of (left andright) first ball contacting portions 15 c that serve as horizontal flatportions are elongated in a direction so as to always intersect thedirection in which the aforementioned tilting load acts on the upperrail 15 (i.e., intersecting the direction of a line tangent to theaforementioned axis), the pair of first ball contacting portions 15 c donot slide in the widthwise direction of the seat track mechanism 13relative to the balls 17 but press the balls 17, which are positionedbelow the pair of first ball contacting portions 15 c, against the pairof ball-supporting recessed portions 16 a-2 so as to become immovablerelative to the lower rail 16 via the balls 17 when such a tilting loadacts on the upper rail 15. This prevents the upper rail 15 from tiltingrelative to the lower rail 16.

In addition, the downward pressing load which acts on the upper rail 15is directly transmitted to the lower rail 16 via the balls 17 with nooccurrence of component force in the left/right direction of the seattrack mechanism 13, so that such a downward pressing load can besecurely relieved and escaped to the vehicle floor 14 side withoutcausing a deformation of the upper rail 15 or the lower rail 16. Namely,in terms of the strength to a vertical load, it is an effective way toform the contacting portions of the upper rail 15 which come in contactwith the balls 17 as the pair of first ball contacting portions 15 c.

Additionally, as described above, the inner peripheral surface of eachball-supporting recessed portion 16 a-2 has a radius of curvaturegreater than the radius of curvature of the spherical surface of eachball 17, and each ball 17 is in point contact with the inner peripheralsurface of the associated ball-supporting recessed portion 16 a-2 to besupported thereby at a single point thereon. This structure has anadvantage also. Namely, unlike the present embodiment of the seat trackmechanism, assuming that each ball 17 is supported by the associatedball-supporting recessed portion 16 a-2 at a plurality of pointsthereon, a variation in the relative position between these pointscauses the amount of movement (stroke) of the upper rail 15 per rotationof the ball 17 to vary. For instance, assuming that each ball 17 issupported by the associated ball-supporting recessed portion 16 a-2 attwo points thereon spaced from each other in the widthwise direction ofthe seat track mechanism 13, the amount of movement of the upper rail 15per rotation of the ball 17 reduces and increases as the distancebetween the two points increases and reduces, respectively. If suchvariations in the amount of movement (stroke) of the upper rail 15 arisebetween the balls 17, the accuracy of movement of the upper rail 15 isaffected by such variations. In a large metal member such as the lowerrail 16, it is difficult to exercise accuracy control so as to keep therelative positions between the contact points of the metal memberrelative to a plurality of balls constant at all times. In contrast, inthe present embodiment of the seat track mechanism, each ball 17 and theassociated first ball contacting portions 15 c are in contact with eachother only at one point therebetween and also each ball 17 and theassociated ball-supporting recessed portion 16 a-2 are in contact witheach other at one point therebetween, so that each ball 17 is heldbetween two points (upper and lower points) thereat. The point ofcontact of each ball 17 with the associated ball-supporting recessedportion 16 a-2 tries to stay at a point farthest from the point ofcontact of the ball 17 with the associated first ball contactingportions 15 c (i.e., at the deepest position in the associatedball-supporting recessed portion 16 a-2), and accordingly, the distancesbetween the upper points and the lower points that hold the balls 17therebetween are uniform and substantially identical to the diameters ofthe balls 17, respectively. As a result, in any of the balls 17, novariation in the amount of movement of the upper rail 15 per rotation ofthe ball 17 occurs, so that a seat track mechanism which ensures slidingmovements of the upper rail 15 relative to the lower rail 16 with a highdegree of accuracy is achieved. In addition, since the dimensionalaccuracies of the balls 17 at the manufacturing stage vary little ascompared with the dimensional accuracies of the upper rail 15 and thelower rail 16, the distance between each first ball contacting portions15 c and the associated ball-supporting recessed portion 16 a-2, whichis fixed by the balls 17, in the vertical direction can be determinedwith a high degree of precision.

Additionally, in the present embodiment of the seat track mechanism 13,the strength of the seat track mechanism 13 in the vicinity of the balls18 has been ensured and the dimensional accuracy thereof in the vicinityof the balls 18 has been improved. As described above, each of the pairof second ball contacting portions 15 e is formed as an inclined flatportion which approaches the rail center in the upward direction fromthe boundary between the second ball contacting portion 15 e and theassociated connecting portion 15 d. Play between the upper rail 15 andthe lower rail 16 is prevented from occurring both in the verticaldirection and the left/right direction (widthwise direction of the seattrack mechanism) by making the balls 18, which are in contact with thepair of second ball contacting portions 15 e, contact the ballinscribing surfaces 16 e of the lower rail 16, each of which is formedby the inner surface of the boundary between one of the side wallportions 16 b and the associated inward-extending flange 16 c. In thepresent embodiment of the seat track mechanism, the angle G (shown inFIG. 4) which represents the raised angle of each second ball contactingportion 15 e relative to a horizontal plane is set at 32 degrees.

If the angle G is too small, the strength for holding the balls 18between the pair of second ball contacting portions 15 e and the pair ofball inscribing surfaces 16 e in the left/right direction is reduced,which makes it easy to cause play between the upper rail 15 and thelower rail 16 in the left/right direction upon a load in the lateraldirection being exerted on the upper rail 15. On the other hand, if theangle G is excessively large, the strength for holding the balls 18between the pair of second ball contacting portions 15 e and the pair ofball inscribing surfaces 16 e in the vertical direction is reduced,which makes it easy to cause play between the upper rail 15 and thelower rail 16 in the vertical direction upon a load in a direction topull up the upper rail 15 being exerted on the upper rail 15. To preventsuch play in the left/right direction and the vertical direction fromoccurring around the balls 18, it is desirable that the angle G be setat an angle between 25 and 40 degrees.

Similar to the above described upper rail 41 in prior art with referenceto FIG. 16, upon a load in a direction to pull up the upper rail 15being imposed on the upper rail 15, component forces urging the upperrail 15 and the lower rail 16 to be deformed in the left/right directionare produced via the second ball contacting portions 15 e that extendobliquely. More specifically, a force urging the pair of vertical wallportions 15 b to approach each other acts on the upper rail 15 while aforce urging the pair of side wall portions 16 b to move away from eachother acts on the lower rail 16. Such component forces in the left/rightdirection increase in proportion to the angle G of each second ballcontacting portion 15 e. For instance, in the prior art shown in FIG.16, the raised angle (which corresponds to the angle G) of each secondinclined portion 41 d of the upper rail 41 relative to a horizontalplane is approximately 56 degrees. The second ball contacting portions15 e, the raised angles of which are smaller than those of the secondinclined portions 41 d of the upper rail 41, can reduce the deformingforce in the left/right direction by a greater degree than the secondinclined portions 41 d of the upper rail 41.

As can be understood from the foregoing, according to the firstembodiment of the seat track mechanism 13, the positional deviation ofthe upper rail 15 relative to the lower rail 16 can be effectivelyprevented from occurring and the upper rail 15 can be effectivelyprevented from wobbling when the upper rail 15 slides relative to thelower rail 16 by a simple and compact structure.

The present invention is not limited solely to the particular embodimentdescribed above; making various modifications to the illustratedembodiment is possible without departing from the spirit and scope ofthe present invention. For example, although the upper rail 15 and thelower rail 16 are provided with the pair of first ball contactingportions (horizontal flat portions) 15 c and the pair of ball-supportingrecessed portions (rotator supporting recesses) 16 a-2, respectively,this relative position is reversible, i.e., the upper rail and the lowerrail can be provided with the rotator supporting recesses and thehorizontal flat portions, respectively.

FIG. 11 shows a vehicle seat assembly 100 including a second embodimentof the seat track mechanism according to the present invention. Thesecond embodiment of the seat track mechanism will be hereinafterdiscussed with reference to FIGS. 12 through 15. Note that elements andportions of the second embodiment of the seat track mechanism which areidentical to those of the first embodiment of the seat track mechanismare designated by the same reference numerals.

The vehicle seat assembly 100 shown in FIG. 11 is provided with a seatcushion 11 that supports the buttocks of an occupant who is seated inthe vehicle seat, and a seatback 12 that supports the back of the seatedoccupant. The vehicle seat assembly 100 is supported by a seat trackmechanism 130 to be movable in the forward/rearward direction relativeto a vehicle floor (floor surface) 14.

As shown in FIGS. 12 and 13, the seat track mechanism 130 is providedwith an upper rail 150 and a lower rail 160 which are secured to thebottom of the seat cushion 11 and the vehicle floor 14, respectively.The upper rail 150 and the lower rail 160 are elongated in theforward/rearward direction of the vehicle, and the position of the seatcushion 11 in the forward/rearward direction can be adjusted by slidingthe upper rail 150 relative to the lower rail 160. The seat trackmechanism 130 is provided between the upper rail 150 and the lower rail160 with a plurality of sliding guide members which ensure smoothsliding movement of the upper rail relative to the lower rail with areduced sliding resistance therebetween while making the lower rail 160support the upper rail 15. Conventional spherical balls (similar to thespherical rotators (17 and 18) of the first embodiment), cylindricalrollers or resin-made slide pieces are adopted as the sliding guidemembers. Although only a pair of rails (the upper rail 150 and the lowerrail 160) is shown in the drawings, the seat track mechanism 130 isprovided with two pairs of rails (each of which includes the upper rail150 and the lower rail 160) installed at different positions in theleft/right direction (lateral direction) of the vehicle seat assembly100 and extend parallel to each other.

As shown in FIG. 14, the lower rail 160 is provided with a bottomportion 160 a, a pair of (left/right) side wall portions 160 b, a pairof inward-extending flanges 160 c and a pair of downward-extendingflanges (deformation preventive portions) 160 d. The bottom portion 160a faces the vehicle floor 14, the pair of side wall portions 160 bextend upwardly from the lateral edges of the bottom portion 160 a, thepair of inward-extending flanges 160 c extend inwardly, toward a centerof the upper rail 150 and the lower rail 160 in the left/right directionwith respect to FIG. 14 (hereinafter referred to as a rail center), fromthe top edges of the side wall portions 160 b, and the pair ofdownward-extending flanges 160 d extend downwardly from the inner edges(edges closer to the rail center) of the pair of inward-extendingflanges 160 c.

The upper rail 150 is provided with a top portion 150 a, a pair of(left/right) first vertical wall portions 150 b, a pair of (left/right)lower-end horizontal wall portions 150 c, a pair of (left/right) secondvertical wall portions 150 d and a pair of (left/right) inclined wallportions 150 e. The pair of first vertical wall portions 150 b extenddownwardly from the lateral edges of the top portion 150 a, the pair oflower-end horizontal wall portions 150 c extend sideways, toward theadjacent side wall portions 160 b, from the bottom edges of the pair offirst vertical wall portions 150 b, the pair of second vertical wallportions 150 d extend upwardly from the outer edges of the pair oflower-end horizontal wall portions 150 c, and the pair of inclined wallportions 150 e extend obliquely upwards, toward the pair ofdownward-extending flanges 160 d, from the top edges of the pair ofsecond vertical wall portions 150 d. In the upper rail 150, the topportion 150 a and the lower-end horizontal wall portions 150 c areformed as horizontal flat portions, and the first vertical wall portions150 b and the second vertical wall portions 150 d are formed as verticalflat portions substantially orthogonal to the horizontal flat portions.Each inclined wall portion 150 e is formed as an inclined flat portionwhich approaches the associated first vertical wall portion 150 b (i.e.,toward the rail center) in the upward direction from the boundarybetween the inclined wall portion 150 e and the associated secondvertical wall portion 150 d.

As shown in FIG. 14, the upper rail 150 is installed into the lower rail160 so that the pair of first vertical wall portions 150 b arepositioned between the pair of downward-extending flanges 160 d with thetop portion 150 a being orientated upwardly and so that the pair ofsecond vertical wall portions 150 d are positioned between the pair ofside wall portions 160 b. In a state where the upper rail 150 and thelower rail 160 are combined, the pair of inclined wall portions 150 eare positioned below the pair of inward-extending flanges 160 c, and theupper end (free end) 150 f of each inclined wall portion 150 e comesinto contact with the associated inward-extending flange 160 c tothereby prevent the upper rail 150 from being detached from the lowerrail 160 when a load in a direction to pull up the upper rail 150 isimposed on the upper rail 150. Namely, in the upper rail 150, the topportion 150 a, which is positioned at the widthwise center of the upperrail 150, and the pair of first vertical wall portions 150 b constitutea central portion of the upper rail 150 having an inverted U-shapedcross section; in addition, the pair of lower-end horizontal wallportions 150 c, the pair of second vertical wall portions 150 d and thepair of inclined wall portions 150 e, which are positioned on both sidesof this central portion of the upper rail 150, respectively, constitutea pair of anti-detaching flanges (anti-detaching portions) which arepositioned below the pair of inward-extending flanges 160 c to beprevented from moving upward beyond the pair of inward-extending flanges160 c, respectively.

A seatbelt anchor (L-shaped anchor plate) 31 to which a seatbelt 30 isconnected is fixed to the top portion 150 a of the upper rail 150. Asshown in FIG. 14, the seatbelt anchor 31 has an L-shaped cross sectionand is provided with a base portion which is fixed to the top portion150 a of the upper rail 150, and an upright portion which projectsupward from the base portion. The arrow F shown in FIG. 14 designatesthe direction of a load which acts on the seatbelt anchor 31 upon theseatbelt 30 being pulled. Due to the structure of the vehicle seatassembly 100, which is structured so that the seatbelt 30 is pulledobliquely upwards relative to the upper rail 150, the direction of thearrow F is inclined toward the center of the widthwise direction(horizontal direction) of the upper rail 150 with respect to a verticaldirection V by an angle θ1 (see FIG. 14).

Each of the pair of inclined wall portions 150 e of the upper rail 150is inclined to approach the adjacent first vertical wall portion 150 bin the upward direction from the boundary between the inclined wallportion 150 e and the associated second vertical wall portion 150 d. Theupper end 150 f of each inclined wall portion 150 e is positioned closerto the widthwise center of the upper rail 150 than the boundary Rbetween the associated lower-end horizontal wall portion 150 c and theassociated second vertical wall portion 150 d. If the angle ofinclination of a line L connecting the boundary R with the upper end 150f of the associated inclined wall portion 150 e relative to the verticaldirection V (angle of inclination of the line L toward the horizontaldirection) is defined as an angle θ2, the angle θ2 is determined so thatthe relationship between the angle θ2 and the angle θ1 of the obliquelyupward direction of the arrow F satisfies the following condition:θ2>θ1. By designing the aforementioned anti-detaching portions of theupper rail 150 to satisfy this condition, an effect which will bediscussed hereinafter is obtained.

The load in the direction of the arrow F which is imposed on theseatbelt anchor 31 is a load urging the seatbelt anchor 31 to bedetached from the top portion 150 a of the upper rail 150, andtherefore, the upper rail 150 is pulled upwards according to this load.However, the upper rail 150 is prevented from moving upward byengagements of the pair of inclined wall portions 150 e with the pair ofinward-extending flanges 160 c. If the angle of inclination θ2 at theanti-detaching portion of the upper rail 150 which is closer to theupright portion of the seatbelt anchor 31 (i.e., the left anti-detachingportion with respect to FIG. 14) and the angle θ1 of the obliquelyupward direction of the arrow F satisfy the aforementioned condition“θ2>θ1”, the inclined wall portion 150 e and the second vertical wallportion 150 d which are closer to the upright portion of the seatbeltanchor 31 (i.e., the left inclined wall portion 150 e and the leftsecond vertical wall portion 150 d with respect to FIG. 14) are actedupon by a component force urging the left inclined wall portion 150 eand the left second vertical wall portion 150 d to tilt (rotate) in adirection toward the rail center (represented by the arrow A1 shown inFIG. 14) about an axis of rotation in the vicinity of the boundary R.This axis of rotation is substantially parallel to the lengthwisedirection of the upper rail 150. A force in the direction of the arrowA2 shown in FIG. 14 which urges the left lower-end horizontal wallportion 150 c and the left second vertical wall portion 150 d to openoutwards (leftwards with respect to FIG. 14) acts on a portion of theupper rail 150 in the vicinity of the boundary R (i.e., in the vicinityof the aforementioned axis of rotation) as a reaction force against thecomponent force in the direction of the arrow A1. Accordingly, acomponent force urging the central portion of the upper rail 150 towiden the width thereof is applied to the central portion of the upperrail 150. This prevents the upper rail 150 from being deformed indirections to make the central portion of the upper rail 150 becomenarrower to bring the pair of first vertical wall portions 150 b closerto each other. Accordingly, a sufficient strength of the upper rail 150can be ensured with no need to provide the upper rail 150 with areinforcing member or the like between the pair of first vertical wallportions 150 b. It should be noted that the upper rail 150 is preventedfrom being largely deformed to a degree that the sliding performance ofthe upper rail 150 may be impaired because each downward-extendingflange 160 d prevents the associated first vertical wall portion 150 bfrom being deformed outwardly (in the direction of the arrow A2 in thecase of the left first vertical wall portion 150 b with respect to FIG.14).

FIG. 15 shows a comparative example of a combination of an upper rail250 and the lower rail 160 which is to be compared with the combinationof the upper rail 150 and the lower rail 160. In this comparativeexample, the lower rail 160 and the seatbelt anchor 31 are identical instructure to those of the second embodiment of the seat track mechanism130, and the upper rail 250 is different in shape from the upper rail150 of the second embodiment of the seat track mechanism 130.

The upper rail 250 is provided with a top portion 250 a, a pair of firstvertical wall portions 250 b, a pair of lower-end horizontal wallportions 250 c and a pair of second vertical wall portions 250 d. Thepair of first vertical wall portions 250 b extend downwardly from thelateral edges of the top portion 250 a, the pair of lower-end horizontalwall portions 250 c extend sideways from the pair of first vertical wallportions 250 b, and the pair of second vertical wall portions 250 dextend obliquely upwards from the pair of lower-end horizontal wallportions 250 c. Although the top portion 250 a, the pair of firstvertical wall portions 250 b and the pair of lower-end horizontal wallportions 250 c are identical in structure to the top portion 150 a, thepair of first vertical wall portions 150 b and the pair of lower-endhorizontal wall portions 150 c of the above described second embodimentof the seat track mechanism 130, the pair of second vertical wallportions 250 d are different in shape from the pair of second verticalwall portions 150 d of the above described second embodiment of the seattrack mechanism 130. Each second vertical wall portions 250 d tiltsoutwardly and upwardly, in a direction away from the widthwise center ofthe upper rail 250 (from the adjacent first vertical wall portion 250b). If the angle of inclination of a line L′ connecting the boundary R′between the left lower-end horizontal wall portion 250 c with respect toFIG. 15 and the upper end (free end) 250 e of the associated secondvertical wall portion 250 d relative to the vertical direction V isdefined as an angle θ3, the condition “θ3<θ1” is satisfied. According tothis structure, upon the upper end 250 e of the left second verticalwall portion 250 d abutting against the adjacent inward-extendingflanges 160 c of the lower rail 160 when a load in the direction of thearrow F is imposed on the upper rail 250, a force in the direction ofthe arrow A3 shown in FIG. 15 which urges the left second vertical wallportion 250 d to tilt outwardly (leftwardly with respect to FIG. 15)about an axis of rotation in the vicinity of the boundary R′ acts on theleft second vertical wall portion 250 d. Thereupon, a force in thedirection of the arrow A4 shown in FIG. 15 which urges the left firstvertical wall portions 250 b to be warped toward the widthwise center ofthe upper rail 250, thus causing the upper rail 250 to be deformed indirections to bring the pair of first vertical wall portions 250 bcloser to each other (to reduce the spacing between the pair of firstvertical wall portions 250 b). Once the width of the central portion ofthe upper rail 25 becomes narrow by this sort of deformation, a requiredstrength of the upper rail 250 cannot be ensured, so that it becomesnecessary to take such measures as installing a reinforcing member orthe like between the pair of first vertical wall portions 250 b of theseatbelt anchor-bearing upper rail 250 to prevent this upper rail frombeing deformed.

In contrast, according to structure shown in FIG. 14, no component forceurging the upper rail 150 from being deformed in directions to make thecentral portion of the upper rail 150 become narrower is produced, sothat a required strength of the upper rail 250 is ensured.

As can be understood from the foregoing, according to the abovedescribed second embodiment of the seat track mechanism, when a load inan upward direction slightly inclined to the vertical direction isimposed on the upper rail 150, the strength of the upper rail 150 andthe sliding performance thereof are not impaired because the seat trackmechanism 130 is provided with the above described anti-detachingportions that are designed so that a force in a direction to bring thepair of first vertical wall portions 150 b closer to each other is notproduced.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1-14. (canceled)
 15. A seat track capable of mounting to a vehicle,comprising: a lower rail mountable to a vehicle floor; an upper railsupported by said lower rail to be slidable relative to said lower rail;and wherein said upper rail comprises: a central portion having aninverted U-shaped cross section; and two anti-detaching portions whichare formed on opposite sides of said central portion in a widthwisedirection thereof to prevent said upper rail from being detached fromsaid lower rail, wherein said two anti-detaching portions apply acomponent force on said central portion so as to urge said centralportion to increase a width thereof by abutting against two flangesformed on said lower rail, respectively, when a pulling load in adirection obliquely upward and lateral is imposed on said upper rail.16. The seat track mechanism according to claim 1, wherein each said twoanti-detaching portions produces a component force urging a free endthereof that abuts against associated one of said two flanges to tilttoward a widthwise center of said upper rail about an axis substantiallyparallel to a lengthwise direction of said upper rail when said pullingload is imposed on said upper rail.
 17. The seat track mechanismaccording to claim 2, wherein said free end of each anti-detachingportion of said upper rail is positioned closer to said central portionof said upper rail than said axis, and wherein an angle of a lineconnecting said free end of each anti-detaching portion with said axisrelative to a vertical direction is greater than an angle of saiddirection of said pulling load.
 18. The seat track mechanism accordingto claim 1, wherein said lower rail comprises two deformation preventiveportions which are positioned adjacent to said opposite sides of saidcentral portion of said upper rail to prevent said width of said centralportion of said upper rail from increasing.
 19. The seat track mechanismaccording to claim 1, wherein said two anti-detaching portions of saidupper rail are provided as a pair which are respectively positioned onopposite sides of said central portion of said upper rail in saidwidthwise direction thereof to be substantially bisymmetrical to eachother.
 20. The seat track mechanism according to claim 1, wherein saidcentral portion and said two anti-detaching portions of said upper railare formed to have an Ω-shaped cross section taken along a planeorthogonal to a direction of sliding movement of said upper railrelative to said lower rail.
 21. The seat track mechanism according toclaim 1, wherein the upper spherical rotators have a smaller diameterthan the lower spherical rotators.